Deck 18: Regulation Of Gene Expression In Prokaryotes

Question 1

What type of regulation occurs when the product of the regulator gene is required to turn on the expression of one or more structural genes?

A) Constitutive control
B) Positive control
C) Negative control
D) Feedback control
E) None of these are correct.

Answer 1

B

Question 2

Which type of genes typically control the enzymes involved in anabolic pathways?

A) Inducible genes
B) Repressible genes
C) Constitutive genes
D) Inducible genes and repressible genes
E) All of these are correct.

Answer 2

B

Question 3

In prokaryotes,genes with related functions often are present in coordinately regulated genetic units called what?

A) Operators
B) Operons
C) Codons
D) Anticodons
E) Regulatory units

Answer 3

B

Question 4

Which level of gene regulation occurs via the action of inducible and repressible genes?

A) Replication
B) Transcription
C) Translation
D) Replication and transcription
E) Replication and translation

Question 5

In a negative,repressible regulatory mechanism,transcription of the structural gene(s)occurs in

A) the absence of the co-repressor, but not in its presence.
B) the absence of the inducer but not in its presence.
C) the absence or presence of the co-repressor.
D) the presence of the co-repressor, but not in its absence.
E) None of these are correct.

Question 6

Which of the following molecules would be made by a constitutive gene?

A) tRNA
B) RNA polymerase
C) Lactose
D) tRNA and RNA polymerase
E) All of these are correct.

Question 7

What type of regulation occurs when the product of the regulator gene is necessary to shut off the expression of structural genes?

A) Constitutive control
B) Positive control
C) Negative control
D) Feedback control
E) None of these are correct.

Question 8

Which of the following statements is false?

A) In an inducible operon, free repressor binds to the operator.
B) In an inducible operon, free repressor cannot bind to the operator.
C) In a repressible operon, free repressor binds to the operator.
D) In an inducible operon, only a repressor-corepressor complex can bind to the operator.
E) In a repressible operon, only the free corepressor can bind to the operator.

Question 9

Enzymes that are involved in catabolic pathways are characteristically controlled by what type of genes?

A) Inducible genes
B) Repressible genes
C) Constitutive genes
D) Inducible genes and constitutive genes
E) All of these are correct.

Question 10

Which of the following would most likely be controlled by a repressible gene?

A) Tryptophan synthesis
B) Lactose catabolism
C) Arabinose catabolism
D) Tryptophan synthesis and lactose catabolism
E) Lactose catabolism and arabinose catabolism

Question 11

Where does the regulator bind in order to control transcription?

A) Promoter
B) Operator
C) Regulator protein binding site
D) Enhancer
E) Silencer

Question 12

Which of the following is not a constituent of an operon?

A) Operator
B) Structural genes
C) Promoter
D) Intron
E) All of these are correct.

Question 13

The process of turning on the expression of genes in response to a substance in the environment is called

A) repression.
B) catabolite repression.
C) glucose effect.
D) induction.
E) positive feedback.

Question 14

Which of the following statements best describes a constitutive gene?

A) A gene that is expressed in the presence of an inducer
B) A gene that is expressed in the absence of a corepressor
C) A gene that is expressed only in the presence of lactose
D) A gene that is expressed continuously.
E) A gene that is under temporal regulation

Question 15

Genes whose expression is turned off in response to a substance in the environment are known as

A) inducible genes.
B) repressible genes.
C) constitutive genes.
D) inducible genes and repressible genes.
E) All of these are correct.

Question 16

Genes encoding products that regulate the expression of other genes are known as

A) positive control genes.
B) negative control genes.
C) regulator genes.
D) transcriptional genes.
E) translatable genes.

Question 17

Which of the following types of molecules controls whether or not a regulator can bind at the appropriate site?

A) Effector molecules
B) Activator molecules
C) Derepressor molecules
D) Effector molecules and derepressor molecules
E) All of these are correct.

Question 18

Genes that are continually being expressed in most cells are referred to as

A) inducible genes.
B) repressible genes.
C) constitutive genes.
D) tRNA genes.
E) mRNA genes.

Question 19

Genes whose expression is turned on in response to a substance in the environment are known as

A) inducible genes.
B) repressible genes.
C) constitutive genes.
D) inducible genes and repressible genes.
E) All of these are correct.

Question 20

Which of the following is a mechanism by which transcription is regulated? 1.Rapid turn-on and turn-off of gene expression in response to environmental changes
2)Preprogrammed circuits or cascades of gene expression
3)Light-switch method

A) 1
B) 2
C) 3
D) 1 and 2
E) 1 and 3

Question 21

Which is true about an operator constitutive (O?)mutation?

A) An O? mutation on the chromosome can affect the expression of structural genes on a plasmid.
B) The O? mutation prevents the expression of a diffusible product that regulates the lac operon.
C) An F' I+P+ O? Z-Y+A-/I+P+O+Z+Y+A+ merozygote expresses the enzymes of the lac operon constitutively.
D) The O? mutations act only in cis.
E) An F' I+P+ O? Z+Y+A+/I+P+O+Z-Y-A- merozygote is inducible for the three enzymes of the lac operon.

Question 22

What happens when a repressor is bound to the operator?

A) RNA polymerase is prevented from transcribing the structural genes in the operon.
B) RNA polymerase transcribes the structural genes in the operon.
C) RNA polymerase increases the rate of transcription.
D) RNA polymerase decreases the rate of transcription.
E) None of these are correct.

Question 23

Which characteristic is exhibited by transcription-termination signals found at the ends of most bacterial operons,such as the trp operon?

A) They encode a nascent RNA with the potential to form hydrogen-bonded hairpin structures.
B) They contain the operator region to which the repressor binds to shut off transcription.
C) They contain the site for the binding of the CAP-cAMP complex to affect catabolite repression.
D) They contain the binding site for the repressor-corepressor complex.
E) They begin with the sequence ATG.

Question 24

The enzyme b-galactosidase is encoded by

A) lacA.
B) lacy.
C) lacZ.
D) lacI.
E) both lacA and lacY.

Question 25

Which statement about catabolite repression is false?

A) Glucose is the preferred energy source for E. coli and represses the utilization of other sugars.
B) The CAP protein is involved in catabolite repression of the lac operon.
C) RNA polymerase is the effector molecule that enables CAP to bind to the promoter.
D) The CAP protein and its effector molecule exert positive control over the transcription of the lac operon.
E) High glucose concentrations decrease the intracellular concentration of the effector molecule of the CAP protein.

Question 26

Which of the following is true regarding the regulation of the trp operon?

A) trpR mutants that lack functional repressor have a tenfold elevated rate of synthesis of the tryptophan biosynthetic enzymes in the presence of tryptophan.
B) Tryptophan is an inducer of the trp operon.
C) trpL deletion mutants in which there is no 162-nucleotide-long leader sequence in the mRNA result in relief of repression and derepression of the trp operon.
D) Premature termination of the trp operon occurs in the presence of tryptophan charged tRNAt?p.
E) In the presence of tryptophan, the ribosome cannot translate past the Trp codons to the leader-peptide termination codon.

Question 27

Which of the following is a constituent of the lac operon promoter?
1)RNA polymerase binding site
2)CAP binding site
3)lac I gene

A) 1
B) 2
C) 3
D) 1 and 2
E) 2 and 3

Question 28

Which of the following substances is the inducer for the lac operon?

A) Lactose
B) Tryptophan
C) cAMP
D) Glucose
E) CAP

Question 29

Which of the following is the best example of derepression?

A) Switching on of the trp operon in the presence of tryptophan
B) Switching off of the trp operon in the presence of tryptophan
C) Switching off of the trp operon in the absence of tryptophan
D) Switching off of the lac operon by the presence of glucose in the medium
E) Switching on of the lac operon in the presence of lactose

Question 30

When are the structural genes in the tryptophan operon transcribed?
1)Tryptophan is in abundance in the environment.
2)Tryptophan is absent from the environment.
3)Tryptophan is present in low amounts in the environment.

A) 1
B) 2
C) 3
D) 1 and 3
E) 2 and 3

Question 31

In the lac operon,what type of control is exhibited by the CAP/cAMP complex?

A) Negative control
B) Positive control
C) Constitutive control
D) Negative control and positive control
E) All of these are correct.

Question 32

Which of the following statements is true regarding the lac operon?

A) The repressor binds to the promoter element.
B) Transcription is initiated by the binding of the inducer to the promoter.
C) The lac operon is unique because it is not subject to catabolite repression.
D) The promoter element is not essential for the transcription of the operon.
E) lacZ, lacY and lacA gene products are synthesized at low levels in the uninduced state.

Question 33

What type of operon is the trp operon?

A) Positive repressible operon
B) Negative repressible operon
C) Positive inducible operon
D) Negative inducible operon
E) Constitutive inducible operon

Question 34

Which of the following best describes the lac operon?

A) Negatively controlled repressible operon
B) Negatively controlled inducible operon
C) Negatively controlled constitutive operon
D) Positively controlled repressible operon
E) Positively controlled inducible operon

Question 35

How do promoter mutations change the expression of the lac operon genes?
1)They change the inducibility of the lac operon.
2)They modify the levels of gene expression in the induced and uninduced state.
3)They change the frequency of initiation of lac operon transcription.

A) 1
B) 2
C) 3
D) 1 and 2
E) 2 and 3

Question 36

In which type of operon does the free repressor binds to the operator,turning off transcription?

A) Inducible operon
B) Repressible operon
C) Constitutive operon
D) Inducible operon and repressible operon
E) All of these are correct.

Question 37

What happens in the lac operon when both lactose and glucose are present in the environment?

A) Transcription of the lac operon structural genes will occur.
B) Transcription of the lac operon structural genes will occur but at a very slow rate.
C) Transcription of the lac operon structural genes will occur at an increased rate.
D) Transcription of the lac operon will not occur because the inducer is not present in the environment.
E) Transcription of the lac operon will not occur because of catabolite repression.

Question 38

Which of the following is false with regard to the operator segment in an operon?
1)Operator regions are contiguous with promoter regions.
2)Operator regions are often located between the promoters and the structural genes that they regulate.
3)Repressors bind to the operator and turn on transcription.

A) 1
B) 2
C) 3
D) 1 and 2
E) 2 and 3

Question 39

The lac repressor (I? gene product)controls the expression of structural genes located where?

A) Cis to the lacI? allele
B) Trans to the lacI? allele
C) Cis to the lacO? allele
D) Cis to the lacI? allele and Trans to the lacI? allele
E) All of these are correct.

Question 40

When temperate bacteriophages,such as phage l,enter the lysogenic pathway,covalently inserting their chromosome into the chromosome of the host,their lytic genes must be

A) turned on.
B) turned off.
C) induced.
D) turned on and induced.
E) None of these are correct.

Question 41

How does catabolite repression stop transcription of the lac operon in the presence of glucose?

Question 42

Where does the phage l repressor bind to prevent transcription of the lytic genes?

A) CI
B) OL
C) OR
D) CI and OL
E) OL and OR

Question 43

Draw a sketch of a simplistic operon with 4 structural genes.

Question 44

Compare how a negative repressible control mechanism and a positive repressible control mechanism work in the presence and absence of a co-repressor.

Question 45

Which of the following is true about regulation of prokaryotic gene expression?

A) Genes such as rRNAs and tRNAs, which specify housekeeping functions, can be repressed or induced as required.
B) Genes that encode enzymes involved in catabolic pathways are always expressed constitutively.
C) Genes that encode anabolic enzymes are not repressible.
D) Transcriptional regulation is the most common mechanism of control in prokaryotes.
E) Translational regulation is the most common mechanism of control in prokaryotes.

Question 46

Which of the following statements regarding regulation of prokaryotic gene expression is incorrect?

A) Accumulation of an end product of a biosynthetic pathway may result in the inhibition of the first enzyme in the pathway.
B) Different regions of an mRNA molecule may degrade at different rates.
C) E. coli cells devote a larger share of energy to the production of ribosomes under starvation conditions than in conditions favorable to growth.
D) Hairpins in the mRNA molecule can decrease translation rates by impeding the migration of ribosomes.
E) Unequal efficiencies of translational initiation are known to occur at the ATG start codons of different genes.

Question 47

Which of the following is a constituent of the phage l repressor?

A) DNA-binding domain
B) Dimerization domain
C) Connector region
D) DNA-binding domain and Dimerization domain
E) All of these are correct.

Question 48

What form of inhibition occurs when the product of a biosynthetic pathway inhibits the activity of the first enzyme in the pathway,rapidly arresting the biosynthesis of the product?

A) Competitive inhibition
B) Feedback inhibition
C) Non-allosteric inhibition
D) Competitive inhibition and feedback inhibition
E) None of these are correct.

Question 49

UV light induces nondefective l prophages to enter the lytic pathway by which of the following mechanisms?

A) SOS response
B) Conversion of RecA to a protease
C) Cleavage of the connector region of the l repressor
D) Prevention of dimerization of the DNA-binding domain of the repressor
E) All of these are correct.

Question 50

Based upon what is known about the regulation of transcription,regulatory mechanisms fall into two general categories.What are these categories and how do they work to aid organisms in cellular growth?

Question 51

Regulatory fine-tuning frequently occurs at the level of translation by:
1)Modulation of the rate of polypeptide chain initiation
2)Modulation of the rate of chain elongation
3)Modulation of the amino acid sequence

A) 1
B) 2
C) 3
D) 1 and 2
E) All of these are correct.

Question 52

How does attenuation help regulate gene expression in the trp operon?

Question 53

Which of the following genes of phage l encodes the repressor?

A) CI
B) OL
C) OR
D) CI and OL
E) OL and OR

Question 54

Negative autogenous regulation refers to

A) inhibition of translation of a specific mRNA by a protein it encodes.
B) inhibition of transcription of a gene by a specific mRNA it encodes.
C) inhibition of the first enzyme of a pathway by the end product of the biosynthetic pathway.
D) inhibition of the synthesis of ribosomes by the accumulation of protein molecules.
E) inhibition of the growth of an organism by the accumulation of toxic waste products.

Question 55

Which of the following is true about the life cycle of phage l?

A) When phage l injects the Cro protein into E. coli it enters the lytic cycle.
B) When phage l injects the repressor into E. coli it enters the lysogenic pathway.
C) Phage l enters the lytic cycle when the repressor occupies the OL and OR sites.
D) Phage l enters the lysogenic pathway when the Cro protein occupies the OL and OR sites.
E) Translation of the cro mRNA is blocked by cro antisense RNA.

Question 56

How is sequential gene expression controlled in bacterial viruses like E.coli phages T7 and T4 and Bacillus subtilis phage SP01?

A) Modifying the DNA topology
B) Sequential binding of a series of repressor molecules
C) Modifying the specificity of RNA polymerase for different promoter sequences
D) Sequential binding of inducer molecules to the repressor
E) None of these are correct.

Question 57

Compare how a negative inducible control mechanism and a positive inducible control mechanism work in the presence and absence of an inducer.